ring_buffer.h

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/*
The MIT License (MIT)
 
Copyright (c) 1999-2022 Mircea Neacsu
 
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
 
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
 */
#pragma once
 
#include <cassert>
#include <memory>
#include <stdexcept>
#include <vector>
 
namespace util {

template <class T> class ring_buffer {
public:
    template <bool C_> class iterator_type {
    public:
        // Following typedefs must exist to allow instantiation of std::iterator_traits
        using difference_type = std::ptrdiff_t;
        using value_type = T;
        using reference = typename std::conditional_t<C_, T const&, T&>;
        using pointer = typename std::conditional_t<C_, T const*, T*>;
        using iterator_category = std::bidirectional_iterator_tag;

        iterator_type()
        : ring(nullptr)
        , pos(0) {}

        reference operator*() {
            if(pos == (size_t)(-1))
                throw std::range_error("Ring buffer iterator at end!");
            return ring->buf[pos];
        }

        const reference operator*() const {
            if(pos == (size_t)(-1))
                throw std::range_error("Ring buffer iterator at end!");
            return ring->buf[pos];
        }

        pointer operator->() {
            if(pos == (size_t)(-1))
                throw std::range_error("Ring buffer iterator at end!");
            return &ring->buf[pos];
        }

        const pointer operator->() const {
            if(pos == (size_t)(-1))
                throw std::range_error("Ring buffer iterator at end!");
            return &ring->buf[pos];
        }

        iterator_type<C_> operator++(int) {
            iterator_type<C_> tmp = *this;
            pos = ring->increment(pos);
            return tmp;
        }

        iterator_type<C_>& operator++() {
            pos = ring->increment(pos);
            return *this;
        }

        iterator_type<C_> operator--(int) {
            iterator_type<C_> tmp = *this;
            pos = ring->decrement(pos);
            return tmp;
        }

        iterator_type<C_>& operator--() {
            pos = ring->decrement(pos);
            return *this;
        }

        bool operator==(iterator_type<C_> const& it) const { return (ring == it.ring) && (pos == it.pos); }

        bool operator!=(iterator_type<C_> const& it) const { return !operator==(it); }

        iterator_type<C_>& operator=(iterator_type<C_> const& rhs) {
            if(this != &rhs) {
                ring = rhs.ring;
                pos = rhs.pos;
            }
            return *this;
        }

        iterator_type<C_> operator+(size_t inc) const {
            iterator_type<C_> tmp = *this;
            tmp.pos = ring->add(pos, inc);
            return tmp;
        }

        iterator_type<C_>& operator+=(size_t inc) {
            pos = ring->add(pos, inc);
            return *this;
        }

        iterator_type<C_> operator-(size_t dec) const {
            iterator_type<C_> tmp = *this;
            tmp.pos = ring->subtract(pos, dec);
            return tmp;
        }

        iterator_type<C_>& operator-=(size_t dec) {
            pos = ring->subtract(pos, dec);
            return *this;
        }

        ptrdiff_t operator-(iterator_type<C_> const& other) const {
            assert(ring == other.ring);
            size_t p1 = (pos != -1) ? pos : (ring->back_idx == ring->front_idx) ? ring->sz : ring->back_idx;
            size_t p2 = (other.pos != -1) ? other.pos : (ring->back_idx == ring->front_idx) ? ring->sz : ring->back_idx;
            if(p1 >= p2)
                return p1 - p2;
            else
                return ring->cap - p2 + p1;
        }
 
    private:
        iterator_type(ring_buffer const* ring_, size_t pos_)
        : ring(ring_)
        , pos(pos_) {}
 
        ring_buffer const* ring;
        size_t pos;
        friend class ring_buffer;
    };
 
    typedef iterator_type<false> iterator;
    typedef iterator_type<true> const_iterator;

    ring_buffer(size_t size)
    : buf(std::unique_ptr<T[]>(new T[size]))
    , cap(size)
    , front_idx(0)
    , back_idx(0)
    , sz(0) {}

    ring_buffer()
    : cap(0)
    , front_idx(0)
    , back_idx(0)
    , sz(0) {}

    ring_buffer(ring_buffer const& other) = delete;

    ring_buffer(ring_buffer&& other) = delete;

    ring_buffer& operator=(ring_buffer const& rhs) = delete;
 
    ring_buffer& operator=(ring_buffer&& rhs) = delete;

    bool operator==(ring_buffer<T> const& other) const noexcept {
        if(cap == other.cap && sz == other.sz) {
            for(size_t i = 0; i < sz; i++) {
                size_t idx1 = (front_idx + i) % cap;
                size_t idx2 = (other.front_idx + i) % other.cap;
                if(buf[idx1] != other.buf[idx2])
                    return false;
            }
            return true;
        }
        return false;
    }

    bool operator!=(ring_buffer<T> const& other) const noexcept { return !operator==(other); }

    operator std::vector<T>() const {
        std::vector<T> v;
        v.reserve(sz);
        std::copy(std::begin(*this), std::end(*this), std::back_inserter(v));
        return v;
    }

    void push_back(T const& item) {
        if(!cap)
            throw std::length_error("ring_buffer: trying to add an element to a buffer of size 0");
        if(sz && back_idx == front_idx)
            throw std::overflow_error("ring_buffer: overflow error");
        sz++;
        buf[back_idx] = item;
        back_idx = (back_idx + 1) % cap;
    }
 
    void push_back(T&& item) {
        if(!cap)
            throw std::length_error("ring_buffer: trying to add an element to a buffer of size 0");
        if(sz && back_idx == front_idx)
            throw std::overflow_error("ring_buffer: overflow error");
        sz++;
        buf[back_idx] = std::move(item);
        back_idx = (back_idx + 1) % cap;
    }

    iterator begin() noexcept { return iterator(this, front_idx); }

    const_iterator begin() const noexcept { return const_iterator(this, front_idx); }

    const_iterator cbegin() const noexcept { return const_iterator(this, front_idx); }

    iterator end() noexcept { return iterator(this, (size_t)(-1)); }

    const_iterator end() const noexcept { return const_iterator(this, (size_t)(-1)); }

    const_iterator cend() const noexcept { return const_iterator(this, (size_t)(-1)); }

    void pop_front() {
        if(!sz)
            throw std::underflow_error("ring_buffer: buffer is empty");
        front_idx = (front_idx + 1) % cap;
        sz--;
    }

    T& front() {
        if(!sz)
            throw std::underflow_error("ring_buffer: buffer is empty");
        return buf[front_idx];
    }

    T const& front() const {
        if(!sz)
            throw std::underflow_error("ring_buffer: buffer is empty");
        return buf[front_idx];
    }

    T& back() {
        if(!sz)
            throw std::underflow_error("ring_buffer: buffer is empty");
        return buf[(back_idx + cap - 1) % cap];
    }

    T const& back() const {
        if(!sz)
            throw std::underflow_error("ring_buffer: buffer is empty");
        return buf[(back_idx + cap - 1) % cap];
    }

    void clear(void) {
        for(size_t i = 0; i < sz; i++) {
            buf[(front_idx + i) % cap].~T();
        }
 
        front_idx = back_idx;
        sz = 0;
    }

    bool empty(void) const noexcept { return (sz == 0); }

    bool full(void) const noexcept { return (sz == cap); }

    size_t capacity(void) const noexcept { return cap; };

    void resize(size_t new_cap) {
        if(new_cap < sz)
            throw std::bad_array_new_length();
        std::unique_ptr<T[]> newbuf(new_cap ? new T[new_cap] : nullptr);
        if(new_cap) {
            for(size_t i = 0; i < sz; i++) {
                newbuf[i] = std::move(buf[(front_idx + i) % cap]);
            }
        } else
            sz = 0;
        cap = new_cap;
        buf.swap(newbuf);
        front_idx = 0;
        back_idx = cap ? (front_idx + sz) % cap : 0;
    }

    size_t size() const noexcept { return sz; }
 
private:
    size_t increment(size_t pos) const noexcept {
        if(cap && pos != (size_t)-1)
            pos = (pos + 1) % cap;
        if(pos == back_idx)
            pos = (size_t)-1;
        return pos;
    }

    size_t decrement(size_t pos) const noexcept {
        if(cap) {
            if(pos == (size_t)-1)
                pos = (back_idx + cap - 1) % cap;
            else if(pos != front_idx)
                pos = (pos + cap - 1) % cap;
        }
        return pos;
    }

    size_t add(size_t oldpos, size_t delta) const noexcept {
        if(cap && oldpos != -1) {
            size_t np = oldpos + (delta % cap);
            if(np >= cap && np >= back_idx + cap)
                np = (size_t)(-1);
            else
                np %= cap;
            return np;
        }
        return oldpos;
    }

    size_t subtract(size_t oldpos, size_t delta) const noexcept {
        if(cap) {
            size_t np = (oldpos == (size_t)-1 ? back_idx : oldpos) - (delta % cap) + cap;
            if(np < front_idx)
                np = front_idx;
            else
                np %= cap;
            return np;
        }
        return oldpos;
    }
 
    std::unique_ptr<T[]> buf;
    size_t front_idx, back_idx, cap, sz;
};
 
} // namespace util